Semiconductor devices for use in networks or digital household electric appliances are being further desired to be sophisticated, multifunctional, and low in power consumption. Accordingly, the trend toward micro-patterning for circuits has been developed, with which micro-sizing of particles has advanced to cause reduction of the production yield. As a result of this, a cleaning step which aims to remove contaminants such as the micro-sized particles and the like is frequently used. As a result, 30-40% of the whole of the semiconductor fabrication process is occupied with the cleaning step.
On the other hand, in cleaning conventionally performed by using a mixed ammonia cleaning agent, damages to the wafer due to its basicity are getting serious with the trend toward micro-patterning for circuits. Therefore, alternation with a dilute hydrofluoric acid-based cleaning agent is taking place.
With this, problems about the damages to the wafer due to cleaning have been solved; however, problems due to an aspect ratio increased with the trend toward micro-processing in the semiconductor devices have become obvious. In other words, a phenomenon where the pattern is collapsed when a gas-liquid interface passes through the pattern is brought about after cleaning or rinsing so as to largely reduce the yield, which has become a significant problem.
The pattern collapse occurs at the time of drawing the wafer out of a cleaning liquid or a rinsing liquid. It is said that the reason thereof is that a difference in height of residual liquid between a part of high aspect ratio and a part of low aspect ratio causes a difference in capillary force which acts on the pattern.
Accordingly, it is expected, by decreasing the capillary force, that the difference in capillary force due to the difference in height of residual liquid is reduced thereby resolving the pattern collapse. The magnitude of the capillary force is the absolute value of P obtained by the equation as represented below. It is expected from this equation that the capillary force can be reduced by decreasing γ or cos θ.P=2×γ×cos θ/S 
(γ: Surface tension, θ: Contact angle, S: Pattern width).
In Patent Publication 1, a technique of replacing water serving as a cleaning agent with 2-propanol before the gas-liquid interface passes through the pattern is disclosed as a method of decreasing γ to suppress the pattern collapse. This method is effective for preventing the pattern collapse; however, a solvent having small γ such as 2-propanol and the like is also small in normal contact angle, which results in the trend to increase cos θ. It is therefore said that there are limitations to adaptable patterns, for example, an aspect ratio of not higher than 5.
Additionally, in Patent Publication 2, a technique directed to a resist pattern is disclosed as a method for decreasing cos θ in order to suppress the pattern collapse. This method is a method of setting a contact angle to around 90° to bring cos θ close to 0 so as to reduce the capillary force to the limit thereby suppressing the pattern collapse. However, the disclosed technique cannot be applied to the present object because: the technique is one directed to the resist pattern or one for reforming a resist itself; and a final removal together with the resist is possible so as not to need the assumption about a method of removing a treatment agent after drying.
Additionally, in Patent Publication 3, there is disclosed a cleaning method including: surface-reforming an unevenly patterned wafer surface with a silicon-containing film; forming a water-repellent protective film on the surface by using a water-soluble surfactant or a silane coupling agent; reducing the capillary force; and thereby preventing the pattern collapse. However, the water repellent used as above is sometimes not sufficient for a water repellency-providing effect.
Additionally, the use of a critical fluid, the use of liquid nitrogen or the like are proposed as the method of preventing the pattern collapse of the semiconductor devices. However, any of these is difficult to apply to a mass-producing process because of its poorer throughput than in conventional cleaning steps, though effective to some extent.